Selective lighting up of segments around Gly,Ala and Ser/Thr in proteins

Direct detection of ¹³C nucleus can be used as a valuable alternative where ¹H detection poses a challenge due to relaxation effects, chemical exchange and poor chemical shift dispersion. In this context, we have designed a suite of 2D ¹³C^α‐detected hNCA experiments that provide sequential correlations of ¹³C^α with ¹⁵N on one hand and efficient spectroscopic labeling of certain groups of residues, namely, Gly, Ala, Ser and Thr, on the other. These residues act as checkpoints in the sequential walk, which in turn offer new possibilities of backbone assignment of small proteins from a set of 2D experiments, thereby providing great economy in terms of spectrometer time. The direct identification of peptide segments around Gly, Ala, Ser and Thr residues along a protein chain will be highly valuable for deriving important information on sites of ligand binding, phosphorylation, inhibitor/substrate binding, understanding protein folding pathways, comprehending local conformational dynamics etc. without having to obtain complete sequence‐specific assignments, which can be time consuming and at times formidable, especially in large proteins. We have illustratively demonstrated the multifaceted applications of these variants of 2D experiments on ubiquitin and M‐crystallin. We foresee that these 2D hNCA experiments will provide economic and efficient strategies for studying the structure and function of proteins. Copyright © 2012 John Wiley & Sons, Ltd.     

Spectroscopic studies and crystal structure of a dimeric Zn(II) complex with diethyl (pyridin-2-ylmethyl)phosphate

The crystal structure of [Zn₂(2-pmOpe)₂Cl₄] (2-pmOpe?=?diethyl (pyridin-2-ylmethyl)phosphate) was determined by X-ray-diffraction method. The compound was also characterized by IR, far-IR, 1H, and ³¹P NMR spectroscopy. In this compound, 2-pmOpe is a bidentate N,O-bridging ligand and Zn(II) are slightly distorted tetrahedral ZnNOCl₂. Zn(II) ions are doubly bridged by the 2-pmOpe ligands, resulting in a dinuclear species. The structure is stabilized by intermolecular C–H?···?O and C–H?···?Cl hydrogen bonds. The spectral properties are in agreement with the structural data.     

Supramolecular assemblies of two piperazine metal-organic bismuth(III) derivatives: a new precursor for the preparation of bismuth(III) oxide bromide nano-structures

Two BiBr₃ supramolecular complexes, [Bi(2-bpmp)Br_2.06Cl_0.94] (1) and [Bi(4-H₂bpmp)Br_4.29Cl_0.71]·H₂O (2) {2-bpmp = N,N′-bis(2-pyridylmethyl)piperazine and 4-bpmp = N,N′-bis(4-pyridylmethyl)piperazine}, were prepared by reaction of bismuth(III) chloride and potassium bromide with two nitrogen donor ligands under thermal gradient conditions using the branched tube method. Compounds 1 and 2 were structurally characterized by single-crystal X-ray diffraction. In monomeric 1, bismuth is coordinated by two pyridyl and piperazine nitrogens of 2-bpmp, and by three halides. Compound 2 is also monomeric but is bonded to only one pyridyl nitrogen. In both compounds, extensive hydrogen-bonding interactions lead to supramolecular networks; in 2, the hydrogen bonds are augmented by π–π stacking interactions. Thermal stabilities of both compounds were studied by thermal gravimetric and differential thermal analyses. Thermal decomposition of nanosized 1 and 2 in air produced BiOBr nanoparticles.     

Organophosphine/phosphite‐stabilized silver(I) complexes bearing N‐acetylbenzamide ligand: synthesis,characterization and potential application in metal organic chemical vapor deposition

New N‐silver(I) acetylbenzamide complexes of type L_n?AgNC₉H₈O₂ (L = PPh₃; n = 1, 2a; n = 2, 2b; n = 3, 2c; L = P(OEt)₃; n = 1, 2d; n = 2, 2e; n = 3, 2f) were prepared. These complexes were obtained in high yields and characterized by elemental analysis, ¹H NMR, ¹³C{H} NMR, ³¹P{H} NMR and IR spectroscopy, respectively. The molecular structure of 2b has been determined by X‐ray single‐crystal analysis in which the silver atom is in a distorted tetrahedral geometry and crystallizes as cis–trans. New N‐silver(I) acetylbenzamide complexes have a four‐membered ring, which could influence their chemical and physical properties and modulate volatility. Metal organic chemical vapor deposition experiments were carried out successfully at 400°C and 450°C using 2e as precursor for the deposition of silver films, respectively. The high‐purity silver film obtained at 400°C is dense and homogeneous. Copyright © 2012 John Wiley & Sons, Ltd.     

Palladium‐catalyzed carbonylative cyclization of β‐bromo‐α,β‐unsaturated carboxylic acids with primary amines leading to N‐alkylmaleimides

Cyclic β‐bromo‐α,β‐unsaturated carboxylic acids are carbonylatively cyclized with primary amines under carbon monoxide pressure in MeCN in the presence of a catalytic amount of PdCl₂(PPh₃)₂ to give N‐alkylmaleimides. Copyright © 2012 John Wiley & Sons, Ltd.     

Anion effects on the phase transition of N‐isopropylacrylamide hydrogels

NMR spectra were collected for poly(N‐isopropylacrylamide) (PNIPAAm) hydrogel using high‐resolution magic angle spinning (HRMAS) after gel pieces were hydrated in the presence of D₂O, NaF, NaCl, and NaI aqueous solutions. Changes in the peak height intensity of the spectra provide quantitative insight into the phase transition process. The thermodynamic values of the phase transition were calculated using a van't Hoff analysis of the NMR data. Unlike the trend observed for decreases in the (LCST), changes in the enthalpy and entropy did not clearly display a linear dependence with respect to salt concentration. Rather, it was observed that increases in salt concentration did not affect the enthalpy and entropy to the extent as the initial change observed between no salt and 100 mM solutions. Finally, the effect of salts on the hysteresis of the rehydrating process was observed. Hysteresis occurs due to the need for hydrophobic interactions to break down before water is able to infiltrate the polymer matrix. NaF stabilizes hydrophobic interactions while NaI destabilize hydrophobic interactions, causing them to break down at higher temperatures. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

14N遥测核四极共振中的偏离共振效应

本文对遥测NQR谱中的偏离共振效应作了较详细地研究,发现¹⁴N谱线的强度随偏离共振效应而变化。当偏离共振强度与射频场强度接近时,测得的谱线强度最大。该效应可用来增强¹⁴N遥测NQR谱仪的灵敏度。上述实验现象在理论上采用脉冲的激发带宽方法作了解释和讨论。